He was born in Padang, Dutch East Indies. During the Weimar Republic he was a member of the German People's Party. In 1933 he joined the Nazi Party, but during the 1930s he began to grow increasingly critical of the regime. He was an acquaintance of Heinrich Himmler as their daughters attended the same school. By 1943 he was aware that Himmler was interested in the idea of negotiating peace behind Adolf Hitler's back. He introduced him to Johannes Popitz who suggested a coup d'état as the war was lost, but Himmler was not interested.
Langbehn was also a friend and adviser to Christabel Bielenberg and her husband Peter. In September 1943 he travelled to Switzerland and met with Allen Welsh Dulles of the Office of Strategic Services to determine the intention of the allies and learnt that they wanted an unconditional surrender from Germany.
- Klemens von Klemperer: German Resistance Against Hitler—The search For Allies Abroad, Clarendon press, Oxford, 1992, USA under Oxford University Press, ISBN 0-19-821940-7.